Imagine in the future that we are able to build a spacecraft that is able to travel 186,250 miles per second. Suppose that a father goes on holiday to a nearby planet. His daughter takes him to the spaceship and bids him farewell. He tells her that he will be back in a year and to keep an eye on the house. When he comes back, he sees a strange old lady living in his house. He asks her, \Who are you and what are you doing in my house?" She says, "I'm your daughter, Dad." What is going here? By the end of this lecture, we will have an answer to this question.